Define the project virtualenv input contract

The accepted input remains: Python 3.x, project directory, and a requirements snippet. Keep parsing and normalization in functions that do not score, train, or call a model. That split lets a test fail the boundary without blaming the core logic. The user-facing decision stays: install project packages without mutating the global interpreter.

.test -x .venv/bin/python && echo 'venv python ready'

Expected evidence: **venv python ready**. If the contract is silent on a bad value, later debugging will look like an algorithm bug when it is really a data bug.

Write one assertion for a neighboring valid input to the project virtualenv so tightening the boundary does not over-reject. Document field names and types the way a teammate would need them on day two of python-virtual-environments—not as comments you plan to delete.

List every field in project dir lab-env/ with requirements.txt containing pandas==2.2.2 and mark each as required, optional, or forbidden. Required fields must fail loudly when missing; optional fields need defaults you can quote in a test; forbidden fields (secrets, raw PII, path escapes) must never be accepted silently. This list is the contract for the project virtualenv.

Add one sentence about encoding, units, or timezones if relevant to Python 3.x, project directory, and a requirements snippet. Contracts that ignore units create “correct” programs that still ship wrong decisions when someone tries to install project packages without mutating the global interpreter.

Write the error string you want for the most likely bad input. Prefer ValueError('threshold out of range')-style messages over generic invalid input. The contract’s job is to make pip installing into the system Python, or activating the wrong venv harder to confuse with a model or algorithm bug later.

At the data contract stage for python-virtual-environments, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about project dir lab-env/ with requirements.txt containing pandas==2.2.2 that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: record global site-packages pandas version (or absence) before creating the venv.

For this page specifically, success looks like malformed inputs rejected with field-named errors while still centering the user decision to install project packages without mutating the global interpreter. If you cannot point to a file, command, or assertion that proves that for the project virtualenv, stay on this page instead of advancing.

Set up a virtual environment

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